Systems using the evaporation of water have been used in arid climates for cooling purposes. A typical installation for cooling a structure includes a motor driven blower for moving air through wetted porous evaporation pads. Such systems are complex and expensive because they typically require a sump with water level controlled by a float valve, and a recirculating pump with a water distribution piping system to keep the evaporative pads moist. The necessity for periodic pad change is a problem.
Evaporative systems have also been used for humidification of greenhouses, and in the printing and weaving industries to maintain a desired moisture content in paper and textile materials. In addition, evaporative systems are useful for mist generation in plant nurseries, produce markets and for dust control and the like. For some of these applications, fog systems incorporating pumps and nozzles have been used. Such fog systems are expensive, difficult to install and often require both filtering and feed water treatment for the removal of minerals.
U.S. Pat. No. 1,626,667 discloses a humidifier with a motor driven conical member for lifting water from a container and supplying the water to a spin disk member having a circumferential rim. Centrifugal force causes particles of water to be thrown from the rim against a surface in the path of a stream of air provided by a fan driven by the motor. The humidifier disclosed in this patent has advantages such as simplicity and low cost not enjoyed by currently used evaporative systems such as those described above. However, the humidifier disclosed in U.S. Pat. No. 1,626,667 is not capable of dispersing a large quantity of extremely fine water particles into an air stream. As a result, the uses to which that device could be put are quite limited.
U.S. Pat. No. 4,458,844 discloses a rotary paint atomizing device in which a rotary disk or bell having a grooved edge configuration is used to atomize paint particles in an electrostatic field. The disk configuration disclosed in that patent would not be well adapted to evaporative apparatus because it is not capable of providing the small particle size desirable for evaporation. In the grooved edge configuration disclosed in U.S. Pat. No. 4,458,844, the grooves lead to a radially oriented end surface of uniform width upon which paint to be atomized collects prior to separation from the disk. As surface tension of the paint collected on this surface is overcome by centrifugal and electrostatic forces, particles of paint are "torn" from the disk. This is intended to provide particle size uniformity, but prevents the formation of particles of a small size.